New porosity model and filtration characteristics of binary mixtures
Empirical equations were used to represent the variation of the cake porosity with the solid compressive or effective pressure. A new porosity model - called cube-contracted model with two parameters has been found to represent data reasonably well. A cube is imagined to contain a particle, and the variation of the size of the cube with the solid compressive pressure is studied. The cube-contracted model generally predicts the porosity values within [plus or minus]0.010 deviation (predicted value - experimental value) or within [plus or minus]2% percentage deviation (predicted value/experimental value - 1). Filteraids may be used to improve filtration processes. Once a filteraid is used, a binary mixture will be formed. The filtration characteristics such as porosity and specific filtration resistance of a binary mixture are determined by the combined effect of many factors. The systematic packing of spheres in beds to simulate real systems is studied. Composition and size ratio play the most important roles in determining the porosity of a binary mixture. If the size ratio is close to 1, the mixture may be taken as an ideal mixture whose components retain their original properties which are independent of the existence of the other material. If the sizes of two components of a binary mixture are widely different, the porosity varies markedly from the ideal behavior. An analogy between the filtration characteristics of binary mixtures and the thermodynamics of binary solutions is studied. Two flow models,one in parallel and the other in series are proposed to calculate the permeability and the specific filtration resistance of a binary mixture in terms of its components. The differential series model is a good representative of the non-filteraid systems. Although the direct application of the models to predicting the specific filtration resistances of the filteraid systems is not sucessful, an alternative method is found to achieve this purpose.